T6354: Get rid of the custom boot type check in version.py (backport #3474)

[mergify]

Change Summary

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T6354

Related PR(s)

Component(s) name

Proposed changes

How to test

vyos@vyos:~$ show version 
Version:          VyOS 1.5-rolling-202405080016
Release train:    current

Built by:         [email protected]
Built on:         Wed 08 May 2024 02:49 UTC
Build UUID:       c2dc10d6-bfe8-4443-8e86-b32ff261a25d
Build commit ID:  bdde6daecd46f3

Architecture:     x86_64
Boot via:         installed image
System type:      KVM guest

Hardware vendor:  QEMU
Hardware model:   Standard PC (i440FX + PIIX, 1996)
Hardware S/N:     
Hardware UUID:    a265716d-3af6-452f-bc42-a9448452fb54

Copyright:        VyOS maintainers and contributors

Smoketest result

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

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This is an automatic backport of pull request #3474 done by [Mergify](https://mergify.com).